The present invention relates to lamps, and relates more particularly to a lamp assembly for Christmas tree light sets which gives an index when the lamp bulb is threaded into position, so as to prevent over pressure of the lamp bulb against the positive metal contact plate. The invention relates also to a method of make a lamp bulb having a patterned outside wall.
Various decorative strings and Christmas tree light sets are well-known and intensively used in western countries as well as most Asian countries during Christmas holidays. When installed, decorative strings and Christmas tree light sets are controlled to flash and to give different colors of light. A lamp assembly for decorative strings or Christmas tree light sets is generally comprised of a lamp socket and a lamp bulb threaded into the lamp socket. The lamp socket comprises a curved positive metal contact plate disposed at the bottom on the inside in a substantially horizontal position, and a straight negative metal contact plate disposed at one side in a substantially vertical position. The curved positive metal contact plate and the straight negative metal contact plate have a respective pointed tip, which pierces the insulator of the electric wire to make contact with a respective conductor in the electric wire. The straight negative metal contact plate further comprises a plurality of vertically spaced raised portions for engagement with the ring contact of the lamp bulb. When the lamp bulb is threaded into the lamp socket, the ring contact and tip contact of the lamp bulb are respectively disposed in contact with the straight negative metal contact plate and the curved positive metal contact plate, and therefore the lamp bulb is electrically connected to the electric wire. However, this structure of lamp assembly is still not satisfactory in function. Because the consumer tends to excessively thread the lamp bulb into the lamp socket, the curved positive metal contact plate will be forced to deform quickly, causing an elastic fatigue. If the springy power of the curved positive metal contact plate deteriorates, it cannot return to its former position after the removal of the lamp bulb, and an electric contact error will occur when a new lamp bulb is installed.
Furthermore, the lamp bulbs of conventional Christmas tree light sets may be differently colored. A colored lamp bulb for a Christmas tree light set made be directly molded from colored melting glass, or made by coating the outer surface of the bulb with a layer of colored paint. However, a colored lamp bulb made according to conventional methods presents only one color, which is monotonous, and cannot attract the consumers' attention.